A general-type of dispenser cathode, such as the type shown in FIG. 1, comprises a porous pellet 3 containing barium-calcium aluminate as the cathode material, a cup 2 for storing the pellet 3, and a sleeve 1 for storing a heater 4.
Among these components, the pellet 3, which is an important component, is manufactured by sintering a high melting point metal powder such as tungsten (W). The pellet 3 has to undergo a high temperature heat treatment because the material itself is a high melting point heat resistant metal.
There are many different methods for manufacturing the pellet. One such method is carried out in such a manner that a mixture of BaCO.sub.3, CaCO.sub.3, and Al.sub.2 CO.sub.3 as the cathode material, or a barium-calcium aluminate obtained by baking such a mixture, is impregnated into a porous pellet made of a heat resistant metal such as tungsten. Another method is carried out such that a mixture prepared by mixing a heat resistant metal powder such as tungsten, molybdenum, or tantalum with a cathode material in a proper ratio is fabricated through compression into a required shape, followed by sintering. (See, for example, U.S. Pat. Nos. 4,737,679 and 4,400,648.)
In such conventional methods, a baking process has to be carried out at a temperature of over 1700.degree. C. However, according to these methods, the electron releasing efficiency is greatly lowered due to the adverse reaction generated by the high temperature treatment. The reason is that Al.sub.2 O.sub.3 (e.g. alumina), which is used as a cathode material, has a very high melting point and its reaction temperature is related to other cathode materials. As long as Al.sub.2 O.sub.3 is used as the cathode material in conventional processes, the high temperature baking process causing the adverse thermal effects cannot be excluded.